1. Field of the Invention
The present invention relates to a plasma processing method using a plasma processing apparatus comprising a plurality of plasma processing chambers for processing samples such as semiconductor wafers, a transfer chamber connected to the processing chambers for transferring samples and a supply system for supplying gas which is the same gas as the transferring gas supplied to the transfer chamber to both the transfer chamber and processing chambers or only to the processing chambers when transferring samples from the transfer chamber to the processing chambers, and specifically, relates to a method for reducing particles attached to the samples during the transferring of semiconductor wafers and other samples into the processing chamber, plasma processing of samples in the processing chambers and transferring of samples out of the processing chambers.
2. Description of the Related Art
In a conventional plasma processing apparatus that utilizes chemical reaction between processing gases and samples such as semiconductor wafers to process the samples, there are drawbacks in that reaction products, which are deposited on inner side walls of the processing chambers when processes generating reaction products are performed continuously, are detached from the walls and are attached to the samples, and in that the atmosphere containing residual components residing in the processing chamber affects the surface of the samples, causing defects such as short circuit of the semiconductor wiring and abnormal process dimension. A plasma processing apparatus further comprises a load lock chamber for transferring samples stored in cassettes to the interior of the apparatus, and generally comprises a transfer chamber adjacent to the load lock chamber for transferring the samples sent into the apparatus to multiple processing chambers disposed adjacent thereto.
However, there has not been any consideration on the flinging up of particles caused by pressure fluctuation within the processing chamber during the continuous processing from when the sample is carried into the processing chamber to when the sample having been subjected to plasma processing is carried out of the processing chamber. In general, gas supplied to the processing chamber as transferring gas when the sample is carried into the processing chamber is stopped when the sample is subjected to plasma processing, high-vacuum evacuation process is performed, and thereafter, processing gas is introduced to the processing chamber to generate plasma to perform plasma processing. Therefore, after stopping the supply of transferring gas before introducing processing gas, the pressure within the processing chamber is reduced from the pressure of the transferring gas supplied to the processing chamber to high-vacuum evacuation pressure, and then fluctuated to the pressure of plasma generation atmosphere of the processing gas, and along with this pressure fluctuation in the processing chamber, the particles deposited on the inner side walls of the processing chamber are flung up. After terminating plasma, the supply of plasma processing gas is stopped and high-vacuum evacuation is performed before supplying transferring gas, so that a similar pressure fluctuation occurs in the processing chamber, causing particles deposited on the inner side walls of the processing chamber to be flung up by pressure fluctuation in the processing chamber similar to when the plasma processing is started.
The art of reducing particles in a plasma processing apparatus is disclosed, for example in Japanese Patent Application Laid-Open Publication No. 2004-281832 (patent document 1), in which gas is supplied from a gas supply unit to either the processing chambers or the transfer chamber or to both the processing chambers and transfer chamber when carrying the samples into and out of the processing chambers, so as to minimize the pressure difference between the chambers and to prevent generation of particles caused by flinging up of particles by turbulent airflow.
The present applicant has proposed, for example in Japanese Patent Application No. 2006-162612 (patent document 2), to switch the scavenging gas supplied to the processing chamber to processing gas, perform plasma processing by generating plasma from processing gas, and after terminating the plasma processing, maintaining plasma while switching from processing gas to scavenging gas. However, the above document does not disclose how a sample is carried into the processing chamber from the transfer chamber while supplying transferring gas into the processing chamber, how plasma is generated from transferring gas, how transferring gas is switched to processing gas while maintaining plasma to perform plasma processing, how processing gas is switched to transferring gas while maintaining plasma by processing gas, and how plasma is terminated and then the sample is carried out of the processing chamber to the transfer chamber.